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21.
Abstract– A new view of disk evolution is emerging from self‐consistent numerical simulation modeling of the formation of circumstellar disks from the direct collapse of prestellar cloud cores. This has implications for many aspects of star and planet formation, including the growth of dust and high‐temperature processing of materials. A defining result is that the early evolution of a disk is crucially affected by the continuing mass loading from the core envelope, and is driven into recurrent phases of gravitational instability. Nonlinear spiral arms formed during these episodes fragment to form gaseous clumps in the disk. These clumps generally migrate inward due to gravitational torques arising from their interaction with a trailing spiral arm. Occasionally, a clump can open up a gap in the disk and settle into a stable orbit, revealing a direct pathway to the formation of companion stars, brown dwarfs, or giant planets. At other times, when multiple clumps are present, a low mass clump may even be ejected from the system, providing a pathway to the formation of free‐floating brown dwarfs and giant planets in addition to low mass stars. Finally, it has been suggested that the inward migration of gaseous clumps can provide the proper conditions for the transport of high‐temperature processed solids from the outer disk to the inner disk, and even possibly accelerate the formation of terrestrial planets in the inner disk. All of these features arising from clump formation and migration can be tied together conceptually in a migrating embryo model for disk evolution that can complement the well‐known core accretion model for planet formation. 相似文献
22.
He Ziguang Armaghani Danial Jahed Masoumnezhad Mojtaba Khandelwal Manoj Zhou Jian Murlidhar Bhatawdekar Ramesh 《Natural Resources Research》2021,30(2):1889-1903
Natural Resources Research - This study combined a fuzzy Delphi method (FDM) and two advanced decision-tree algorithms to predict air-overpressure (AOp) caused by mine blasting. The FDM was used... 相似文献
23.
Alexandre Corgne Shantanu Keshav Bernard J. Wood Yingwei Fei 《Geochimica et cosmochimica acta》2008,72(2):574-589
We present the results of new partitioning experiments between metal and silicate melts for a series of elements normally regarded as refractory lithophile and moderately siderophile and volatile. These include Si, Ti, Ni, Cr, Mn, Ga, Nb, Ta, Cu and Zn. Our new data obtained at 3.6 and 7.7 GPa and between 2123 and 2473 K are combined with literature data to parameterize the individual effects of oxygen fugacity, temperature, pressure and composition on partitioning. We find that Ni, Cu and Zn become less siderophile with increasing temperature. In contrast, Mn, Cr, Si, Ta, Nb, Ga and Ti become more siderophile with increasing temperature, with the highly charged cations (Nb, Ta, Si and Ti) being the most sensitive to variations of temperature. We also find that Ni, Cr, Nb, Ta and Ga become less siderophile with increasing pressure, while Mn becomes more siderophile with increasing pressure. Pressure effects on the partitioning of Si, Ti, Cu and Zn appear to be negligible, as are the effects of silicate melt composition on the partitioning of divalent cations. From the derived parameterization, we predict that the silicate Earth abundances of the elements mentioned above are best explained if core formation in a magma ocean took place under increasing conditions of oxygen fugacity, starting from moderately reduced conditions and finishing at the current mantle-core equilibrium value. 相似文献
24.
Geo-limis - a decision support system for minimizing locust impact in republic of kazakhstan 总被引：1，自引：0，他引：1
Dutta D. Bhatawdekar S. Chandrasekharan B. Sharma J. R. Adiga S. Wood Duncan Mccardle Adrian 《Journal of the Indian Society of Remote Sensing》2004,32(1):25-47
Desert locusts (DL) are serious problem during April to August in the deserts and semi-deserts of Republic of Kazakhstan and
causing extensive crop damage. There is no institutional and functional mechanism to forecast the habitat of locusts and most
of the area remains unnoticed after laying eggs. The key to improve DL forecasting and control depends on the collection and
generation of historical database on locusts, weather and habitat from affected region. Looking at the problem, a Spatial
Decision Support Systems (DSS) has been developed on ARC/INFO GIS with ergonomic user interface for ingestion and subsequent
analysis of locust related information vis-à-vis bio-physical and climatic data acquired from various satellite sensors and
hydromet weather server respectively, to identify high frequency breeding areas well before the physiological development
is completed. Weather based analytical models for physiological development of DL has been dovetailed with the SDSS for facilitating
historic and present data analysis in relation to locust activity. This has augmented the surveying capability and better
forecasting. 相似文献
25.
Natural Hazards - In the Indian Himalayan region, landslide is one of the most recurring natural disasters intimidating human lives and is detrimental to infra-structures,... 相似文献
26.
Murlidhar Bhatawdekar Ramesh Kumar Deepak Jahed Armaghani Danial Mohamad Edy Tonnizam Roy Bishwajit Pham Binh Thai 《Natural Resources Research》2020,29(6):4103-4120
Natural Resources Research - Blasting is an economical technique for rock breaking in hard rock excavation. One of its complex undesired environmental effects is flyrock, which may result in human... 相似文献
27.
Zhou Jian Koopialipoor Mohammadreza Murlidhar Bhatawdekar Ramesh Fatemi Seyed Alireza Tahir M. M. Jahed Armaghani Danial Li Chuanqi 《Natural Resources Research》2020,29(2):625-639
Flyrock is one of the most important environmental issues in mine blasting, which can affect equipment, people and could cause fatal accidents. Therefore, minimization of this environmental issue of blasting must be considered as the ultimate objective of many rock removal projects. This paper describes a new minimization procedure of flyrock using intelligent approaches, i.e., artificial neural network (ANN) and particle swarm optimization (PSO) algorithms. The most effective factors of flyrock were used as model inputs while the output of the system was set as flyrock distance. In the initial stage, an ANN model was constructed and proposed with high degree of accuracy. Then, two different strategies according to ideal and engineering condition designs were considered and implemented using PSO algorithm. The two main parameters of PSO algorithm for optimal design were obtained as 50 for number of particle and 1000 for number of iteration. Flyrock values were reduced in ideal condition to 34 m; while in engineering condition, this value was reduced to 109 m. In addition, an appropriate blasting pattern was proposed. It can be concluded that using the proposed techniques and patterns, flyrock risks in the studied mine can be significantly minimized and controlled.
相似文献28.
Strongly silica-poor (ne-normative), mafic alkaline lavas generally represented by olivine nephelinites, nephelinites, melilitites, and olivine melilitites
have erupted at various locations during Earth's history. On the basis of bulk-rock Mg#, high concentrations of Na2O, TiO2, and K2O, and trace element geochemistry, it has been suggested that these lavas represent low-degree melts that have undergone little
crystal fractionationen route to the surface. Many of these lavas also carry high-pressure mantle material in the form of harzburgite, spinel lherzolite,
and variants of websterite xenoliths, and rare garnet-bearing xenoliths. However, phenocryst phases instead indicate that
these magmas cooled to variable extents during their passage. We note subtle, yet important, differences in terms of CaO,
Al2O3, CaO/AlP2O3, and CaO/MgO. High-pressure experimental melting studies in CMAS-CO2 (3-8 GPa) and natural lherzolitic systems (3GPa) demonstrate that at an isobar increasing F leads to a moderate decrease
in CaO + MgO, whereas CaO/MgO and CaO/Al2O3 sharply decrease. Relatively high CaO/Al2O3 indicates melting in the presence of garnet (>- 85 km). Studies also demonstrate that CO2-bearing lherzolitic systems, when compared with anhydrous ones, also have higher CaO content in the coexisting melt at a
given P and T. Comparison of the bulk-rock major-element chemistry of silica-poor, mafic alkaline lavas with experimentally
determined high-pressure melts indicates that melting of anhydrous mantle lherzolite or garnet pyroxenite is not able to explain
many of the major element systematics of the lavas. However, high-pressure partial melts of carbonated lherzolite have the
right major element trends. Among ocean islands, lavas from Samoa and Hawaii are perhaps the products of very low degree of
partial melting. Lavas from Gran Canaria and Polynesia represent products of more advanced partial melting. On continents,
lavas from South Africa and certain localities in Germany are the products of a very low degree of partial melting, and those
from Texas and certain other localities in Germany are products of a slightly more advanced degree of partial melting of a
carbonated lherzolite. Lavas from Deccan, Czech Republic, and Freemans Cove are the products of even more advanced degree
of partial melting. The mere presence of mantle xenoliths in some of these lavas does not necessarily mean that the erupted
lavas represent direct mantle melts. 相似文献
29.
Ramesh Murlidhar Bhatawdekar Yazdani Bejarbaneh Behnam Jahed Armaghani Danial Mohammed Ahmed Salih Tonnizam Mohamad Edy 《Natural Resources Research》2021,30(2):1865-1887
Natural Resources Research - In surface mines and underground excavations, every blasting operation can have some destructive environmental impacts, among which air overpressure (AOp) is of major... 相似文献